Byline: V. RajMohan, E. Mohandas "The hypothalamus, the anterior thalamic nucleus, the cingulate gyrus, the hippocampus and their interconnections, constitute a harmonious mechanism which may elaborate the functions of central emotion as well as participate in the emotional expression." James Papez, 1937 The limbic system consists of the phylogenetically old limbic lobe and other subcortical structures and their connections. Although not empirically proven, the limbic system is a functional concept which may be employed to explain various brain functions.[sup] [1] History Paul Pierre Broca in 1878 spoke of ' le grand lobe limbique' or the great limbic lobe and applied the term "limbic" (from the Latin limbus for border) to the curved rim of the cortex which incudes the cingulate and the parahippocampal gyri. However, its putative role in emotion was elaborated by the American physician, James Papez in 1937 in the seminal paper titled 'A proposed mechanism of emotion'. This anatomical model is referred to as the Papez circuit.[sup] [2] Yakovlev in 1948 proposed Yakovlev's circuit in the control of emotion involving the orbitofrontal, insular and anterior temporal lobe cortex, the amygdala and the dorsomedial nucleus of thalamus.[sup] [3] In 1952, Paul D. MacLean coined the term "limbic system" to describe Broca's limbic lobe and related subcortical nuclei as the collective neural substrate for emotion.[sup] [1] MacLean was also instrumental in proposing and defining the Triune concept of the brain. MacLean's evolutionary "Triune brain theory" proposed that the human brain was in reality three brains in one: the R-complex (reptilian complex), the limbic system and the neocortex.[sup] [4] The concept of the limbic system has since been further expanded and developed by Nauta, Heimer and others. Components of the Limbic System There is no universal agreement on the total list of structures, which comprise the limbic system. The brain regions that constitute the limbic system are: *Limbic cortex i. Cingulate gyrus ii. Parahippocampal gyrus *Hippocampal formation i. The dentate gyrus ii. Hippocampus iii. Subicular Complex *Amygdala *Septal area *Hypothalamus These structures form a complex network for controlling emotion.[sup] [5] Limbic lobe The limbic lobe situated at the inferomedial aspect of the[sup] cerebral hemispheres, consists of two concentric gyri surrounding[sup] the corpus callosum. Broca proposed that the larger outer gyrus[sup] be named[sup] " limbic gyrus" and the smaller inner one "the intralimbic gyrus".[sup] The limbic gyrus (limbic lobe) consists of the[sup] isthmus of the cingulate gyrus, the parahippocampal gyrus (both of which are continuous via a bundle of white matter called "cingulum") and the subcallosal area.[sup] [6] The cingulate gyrus (Latin = Belt ridge) dorsal to the corpus callosum is heavily interconnected with the association areas of the cerebral cortex. The parahippocampal gyrus in the medial temporal lobe contains several distinct regions, the most important being the entorhinal cortex (ERC). The ERC funnels highly processed cortical information to the hippocampal formation and serves as its major output pathway.[sup] [5] The hippocampal formation Hippocampal formation in the temporal lobe has three distinct zones: *The dentate gyrus *The hippocampus proper *The subiculum Embryologically, the hippocampal formation is an extension of the medial edge of the temporal lobe. The entire hippocampal formation has a length of about 5 cm from its anterior end at the amygdala to its tapering posterior end near the splenium of the corpus callosum.[sup] [5] Dentate gyrus The dentate gyrus is composed of three layers: an outer acellular molecular layer, a granular middle layer and an inner polymorphic layer. …